Optical recording elements comprising novel metallized azo ether dyes

ABSTRACT

Metallized azo ether dyes having an azo group linking a substituted 3-hydroxypyridine nucleus to a phenyl nucleus are disclosed. The phenyl nucleus has an ether substituent ortho to the azo group. The phenyl nucleus is free of strong electron withdrawing substituents. The dyes are useful in optical recording elements.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is cross referenced to the following titledapplication filed by the inventors of the present application on thesame day as the present case:

U.S. Ser. No. 08/881,967, filed Jun. 25, 1997 now U.S. Pat. No.5,821,029, entitled OPTICAL RECORDING ELEMENTS CONTAINING MIXTURES OFMETALLIZED AZO ETHER AND CYANINE DYES

FIELD OF THE INVENTION

The present invention relates to dyes and optical recording elementsgenerally and DVD optical recording elements in particular.

BACKGROUND OF THE INVENTION

Optical recording elements for recording and storing digital informationare known. One of the currently popular optical recording element is thecompact disc or CD. CDs and recordable CDs (CD-Rs) have transformed thepersonal entertainment, personal computer and data storage industries.CDs and CD-Rs have made it possible to store enormous amounts of musicor data on inexpensive, reliable, mass produced media.

Digital Versatile Disc (DVD) and recordable DVD (DVD-R) opticalrecording elements are being developed. For reasons stated below theseelements have significantly greater storage capacity than CDs.

In CDs and DVDs digital information is stored in the form of lowreflective marks on an otherwise reflective background. In this formatthe optical information is in the form of read only memory or ROM.Optical information is not recorded in real time, but is produced bypress molding. In a typical process a substrate is stamped with a mastercontaining the digital information in an embossed form. The stampedsubstrate, bearing deformations caused by the embossed master, is coatedwith a reflective layer and then with a protective layer. In the stampedsubstrate areas having the deformations the reflectivity is lower thanin undeformed areas.

DVD elements have significantly more stringent requirements than CDs.The recording wavelength is 635 nm instead of 780 nm; playbackwavelengths are 635 nm and 650 nm instead of 780 nm; numerical apertureof the read head is 0.6 instead of 0.5; the track pitch is 0.8 μminstead of 1.6 μm and the minimum mark length is 0.44 μm instead of 0.83μm. These changes increase the data storage capacity significantly. InDVD the thickness of the stamped substrate is only 0.6 mm instead of 1.2mm. However a total substrate thickness of 1.2 mm is required to makeDVD elements physically stiffer and the same dimension as the popularCDs. This makes them useful in the current population of DVD modified CDplayers. Generally this is satisfied by forming a laminate structurethat includes a substrate on opposite sides of other DVD requiredlayers. Each substrate may be stamped with stored information or onlyone is so stamped.

It is sometimes desirable to produce an optical recording element thatcan be recorded in real time. CD-R elements having this capability areknown. Such elements have dye containing optical recording layers coatedonto a grooved substrate. The recording layer is coated with areflectivity layer and then a protective layer. Exposure of the elementto a laser recording beam operating in the region of 780 nm forming arelatively low reflective mark.

U.S. Pat. No. 5,500,325 to Chapman et al. discloses dye mixtures foroptical recording layers. The mixtures comprise metallized azo etherdyes and a second dye. U.S. Pat. No. 5,426,015 discloses opticalrecording layers comprising metallized azo dianions with two cationicdye counterions.

DVD-R elements are constructed and used similarly to CD-R elements.However in DVD-R elements the shorter recording and playback wavelengthsnecessitate the development of new and different dye based opticalrecording layers.

SUMMARY OF THE INVENTION

The present invention provides a metallized azo ether dye having an azogroup linking a substituted 3-hydroxypyridine nucleus to a phenylnucleus wherein the phenyl nucleus has an ether substituent ortho to theazo group and said phenyl nucleus is free of strong electron withdrawinggroups (such as nitro and alkylsulfonyl).

The present invention also provides optical recording element having, atransparent substrate and on the surface of said substrate, a recordinglayer, a light reflecting layer; wherein the recording layer comprises(a) a metallized azo ether dye having an azo group linking a substituted3-hydroxypyridine nucleus to a phenyl nucleus wherein the phenyl nucleushas an ether substituent ortho to the azo group and said phenyl nucleusis free of strong electron withdrawing groups and (b) has, whenunrecorded, a refractive index at a selected wavelength from 400 to 660nm, comprising a real part (n) greater than 1.8 and an imaginary part(k) less than 0.3.

The dyes have good recording sensitivity and excellent light and darkstability in optical recording elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a DVD optical recording element having a single opticalrecording layer.

FIG. 2 presents a DVD optical recording element having two opticalrecording layers.

DETAILED DESCRIPTION OF THE INVENTION

Novel metallized azo ether dyes included in this invention include thosehaving the formula (I):

wherein;

R₁ represents hydrogen or an alkyl of from 1 to 6 carbons;

R₂ represents hydrogen, an alkyl of from 1 to 6 carbons or alkoxy with 1to 10 carbons or halogen;

R₃ is free of strong electron withdrawing groups and representshydrogen, an alkyl of from 1 to 10 carbons or alkoxy with 1 to 10carbons or halogen;

R₄ represent an alkyl of from 1 to 10 carbons, a substituted orunsubstituted benzyl; an aryl of from 6 to about 10 carbons or a hetarylof from 5 to about 10 carbons;

The general preparation of the dyes of this invention is illustrated bythe following preparation of a nickel complex of2-amino-3-hydroxy-6-(2-{2-ethoxyethoxy}phenylazo)pyridine:

2-({2-Ethoxyethoxy})aniline (2.1 g) was dissolved in a mixture of water(14 mL) and concentrated HCl(4 mL) and the solution cooled in ice. Asolution of sodium nitrite (0.72 g) in water (2 mL) was added slowly andthe mixture stirred for 1 hour. The diazonium solution was added to acooled solution of 2-amino-3-hydroxypyridine (1.1 g) and sodium acetate(15 g) in methanol (100 mL). After 2 hours the reaction mixture wasdiluted with water and the product filtered off and washed with water.The dried dye was recrystallized from ethyl acetate. The yield was 2.3g. of material having an nmr spectrum in agreement with the desiredproduct. Conversion to the metallized dye was carried out by refluxingthe above dye (2.0 g) with nickel acetate (0.82 g) in methanol (30 mL)for 4 hours. The solution was cooled and the product filtered off. Theyield was 2.1 g. λ max 562 nm ε=8.51×10⁴. Representative compoundswithin formula I are presented in Table 1.

TABLE 1 Metallized Azo Ether Dyes

Dye No R₁ R₂ R₃ R₄ 1 H H H CH₃ 2 H H H CH₂CH₃ 3 H H H (CH₂)₇CH₃ 4 H H H(CH₂)₂OCH₂CH₃ 5 H H m-OCH₃ CH₃ 6 H H p-OCH₃ CH₃ 7 H H H

8 H H H (CH₂)₂CH₃ 9 H H H (CH₂)₃CH₃ 10  H H H CH₂CH(CH₃)₂ 11  CH₃ H HCH₂CH₃ 12  CH₃ H H (CH₂)₂CH₃ 13  H CH₂CH₃ H CH₂CH₃ 14  CH₂CH(CH₃)₂ H HCH₂CH₃ 15  H H m-CH₂CH(CH₃)₂ CH₂CH₃ 16  H H m-CH₃ CH₂C₆H₅

The indices of some metallized azo ether dyes from Table 1 are listed inTable 2 below.

TABLE 2 Indices of the metallized azo ether dyes Azo Dye No. Index (n/k)at 650 nm 1 2.12-0.13i 2 2.24-0.15i 3 2.08-0.24i 4 2.06-0.10i 62.04-0.08i

Optical Recording Elements

Broadly optical elements provided by the invention comprise a lighttransmitting, typically pregrooved substrate, a dye recording layeroverlaying the substrate, a light reflective layer overlaying the lightabsorptive layer and a protective layer overlaying the light reflectivelayer. The recording process will produce marks of lower reflectivitythan the unmarked areas of the disk when written and read with a diodelaser emitting between 400 and 660 nm. The substituents on the dyemolecules are selected such that the real part of the complex refractiveindex (n) of the unwritten recording layer measured with a light sourcehaving a selected wavelength from 400 to 660 nm is greater than 1.8 andthe imaginary part (k) is less than 0.3.

Several different layer configuration embodiments are possible for DVDoptical recording elements. Two embodiments are presented in FIGS. 1 and2.

In the FIG. 1 embodiment the DVD element comprises the following layerarrangement:

(a) a transparent grooved substrate (1) having a groove width of from100 to 800 nm; a groove depth of 30 to 270 nm; and a groove pitch of 0.5to 1.8 μm, usually 0.8 μm or below.

(b) an optical recording layer (2) comprising a metallized azo ether dyehaving an azo group linking a substituted 3-hydroxypyridine nucleus to aphenyl nucleus wherein the phenyl nucleus has an ether substituent orthoto the azo group. The unrecorded recording layer has a refractive index,at a selected wavelength from 645 to 655 nm, comprising a real part (n)greater than 1.8 and an imaginary part (k) less than 0.3.

(c) a light reflecting layer (3).

(d) a protective layer (4).

(e) an adhesive layer (5).

(f) a protective layer (6).

(g) a reflective layer (7).

(h) a substrate (8).

In the embodiment presented in FIG. 1 one or more of layers (d), (f) and(g) may be omitted.

In the FIG. 2 embodiment the DVD element comprises the following layerarrangement:

(a) a transparent grooved substrate (1) having a groove width of from100 to 800 nm; a groove depth of 30 to 270 nm; and a groove pitch of 0.5to 1.8 μm, usually 0.8 μm or below.

(b) an optical recording layer (2) comprising a metallized azo ether dyehaving an azo group linking a substituted 3-hydroxypyridine nucleus to aphenyl nucleus wherein the phenyl nucleus has an ether substituent orthoto the azo group. The unrecorded recording layer has a refractive index,at a selected wavelength from 645 to 655 nm, comprising a real part (n)greater than 1.8 and an imaginary part (k) less than 0.3.

(c) a light reflecting layer (3).

(d) a protective layer (4).

(e) an adhesive layer (5).

(f) a protective layer (6).

(g) a reflective layer (7).

(h) an optical recording layer (2) comprising a metallized azo ether dyehaving an azo group linking a substituted 3-hydroxypyridine nucleus to aphenyl nucleus wherein the phenyl nucleus has a ether substituent orthoto the azo group. The unrecorded recording layer has a refractive index,at a selected wavelength from 645 to 655 nm, comprising a real part (n)greater than 1.8 and an imaginary part (k) less than 0.3.

(i) a transparent grooved substrate (8) having a groove width of from100 to 800 nm; a groove depth of 30 to 270 nm; and a groove pitch of 0.5to 1.8 μm, usually 0.8 μm or below.

In some FIG. 2 embodiments one or both of the protective layers (d) and(f) may be omitted.

The substrate may be any transparent material that satisfies themechanical and optical requirements. For DVD-R substrates the requiredgroove specifications are mentioned in the description of FIGS. 1 and 2above. The preferred material is polycarbonate, other materials areglass, polymethylmethacrylate and other suitable polymeric materials.

The preparation of the optical recording elements of the invention isachieved by spin coating of the dye, with or without addenda, from asuitable solvent onto a transparent substrate. For coating, the dyemixture, with or without addenda, is dissolved in a suitable solventsuch that the dye is 20 or fewer parts by weight to 100 parts of solventby volume. The dye recording layer of the element is then overcoatedwith a metal reflective layer under reduced pressure by resistiveheating or a sputter method and finally overcoated with a protectiveresin.

Coating solvents for the dye recording layer are selected to minimizetheir effect on the substrate. Useful solvents include alcohols,hydrocarbon halides, cellosolves, ketones. Examples of solvents are2,2,3,3-tetrafluoropropanol, tetrachloroethane, dichloromethane, methylcellosolve, ethyl cellosolve, 1-methoxy-2-propanol,4-hydroxy-4-methyl-2-pentanone. Preferred solvents are alcohols sincethey have the least effect on the preferred polycarbonate substrates.Mixtures containing these solvents can also be used.

Useful addenda for the recording layer include stabilizers, surfactants,binders and diluents.

The reflective layer can be any of the metals conventionally used foroptical recording materials. Useful metals can be vacuum evaporated orsputtered and include gold, silver, aluminum, copper and alloys thereof.

The protective layer over the reflective layer is similarly conventionalfor this art. Useful materials include UV curable acrylates.

An intermediate layer, to protect the metal layer from oxidation, canalso be present.

In DVD elements the adhesives can be applied using screen printing, hotroller and spin coating methods. The adhesives to form the laminatesinclude UV curable adhesives, hot melt adhesives, UV initiated cationicpolymeric adhesives, pressure sensitive adhesives and acrylates.

The refractive index values for unrecorded recording layers weredetermined by coating a layer of the dye on a silicon wafer. Therefractive index values (n and k) were measured by a Variable AngleSpectroscopic Ellipsometer (VASE) manufactured by J. A. Woollan Company.

The following examples demonstrate the recording sensitivity and lightand dark stability of the optical recording layers provided by thisinvention.

For each of the dyes studied a complete DVD recording element accordingto FIG. 1 was prepared as presented in the examples.

EXAMPLE 1

In this example a DVD type optical recording element according to FIG. 1was prepared and tested. A first assembly was prepared comprising, inthe following order, substrate, recording layer, reflective layer andprotective layer. The second assembly comprised, in the following order,a substrate, a reflecting layer and a protective layer. This firstassembly was then laminated with an adhesive to the second assembly,protective layer to protective layer. The dye for the recording layerwas selected from Table 1.

First Assembly

A polycarbonate substrate having a thickness of 0.6 mm, a diameter of120 mm and a center hole diameter of 15 mm with a spiral groove on itssurface with a width of 300 nm, a depth of 140 nm and a pitch of 0.8 mm,was made by injection molding.

To form the optical recording layer 1 part by weight of dye 1 wasdissolved with ultrasound at room temperature in 1 hour in 50 parts of2,2,3,3-tetrafluoropropanol by volume. The solution was filtered througha 0.2 μm filter. The solution was spin coated on the surface of thesubstrate to an overall optical density of 0.51 at 526 nm. The coatingwas dried at 60° C. for 30 minutes.

A gold reflective layer was deposited by a sputter process between 19.05mm and 59.29 mm radii on the dye recording layer to about 40 nmthickness. For the deposition a Uniline 3000 made by First LightTechnologies equipped with a Torus 10 DC magnetron source was used.Ionized argon gas was the gold carrier gas at 6000WS (+/−1000)deposition energy level.

A protective layer(DaiNippon Daicure SD-220) was spin coated over thegold reflective layer to a thickness of 7 to 11 mm. The protective layerwas UV cured by the Fusion F300 series cure station with an ‘H+’ bulb in2.6 seconds.

Second Assembly

This assembly was prepared as in the first assembly using the substrate,reflective and protective layers.

The completed DVD element was prepared by laminating the first andsecond assemblies together through their respective protective layers.The laminate was formed by applying Sony SK7000 UV curable adhesive withan Autoroll 560 print head programmed for individual discs. The adhesivewas silk-screened on to the protective layer of each assembly through a305 mesh Kodak DOC (durable overcoat) silk-screen with a 90 durometersqueegee used at a 70 degree angle. Each assembly was UV cured at a rateof 10.668 meters per minute under a Fusion 450 UV lamp 25.4 cm “H” bulb.The two assemblies were mated adhesive to adhesive on a locating spindleand 35.6 N (8 pound force) was applied for 2 minutes. The thus formedDVD element was allowed to remain a rest on the spindle for 5 minutes(which resulted in about 90% cure). To be fully cured before testing,the DVD element was left to stand for 24 hours.

To test the DVD element a test system consisting of an optical head witha 635 nm laser, a 0.6 NA lens, push-pull tracking, and ½ aperturefocusing was used. The optics used circularly polarized light to reducelaser feedback effects. Recording and play back were carried out withthe same laser at 3.84 m/s rotational speed. The read power was kept at0.5 mW. Single frequency marks were recorded with a 1.61 μm mark lengthat 7 mW write power thereby forming marks of lower reflectivity than theunmarked area when examined with a light source emitting at 635 nmlight. When the marks were read with the read laser, through a 30 kHzbandpass filter centered at the mark carrier frequency for thisrecording layer, a CNR (carrier to noise ratio) of 53 dB was obtained.

EXAMPLE 2

In this example the same disk substrate solvent, solution concentration,filter, spin coater, drying conditions, gold deposition process, lacquerlayer application, lamination and testing procedure were used as in thefirst example. Dye 2 was coated on the grooved surface of the substrateto an overall optical density of 0.51 at 526 nm. When written with 8 mWwrite power a 62 dB CNR was obtained on reading.

EXAMPLE 3

In this example the same disk substrate solvent, solution concentration,filter, spin coater, drying conditions, gold deposition process, lacquerlayer application, lamination and testing procedure were used as in thefirst example. Dye 3 was coated on the grooved surface of the substrateto an overall optical density of 0.45 at 526 nm. When written with 8 mWwrite power a 59 dB CNR was obtained on reading.

EXAMPLE 4

In this example the same disk substrate solvent, solution concentration,filter, spin coater, drying conditions, gold deposition process, lacquerlayer application, lamination and testing procedure were used as in thefirst example. Dye 4 was coated on the grooved surface of the substrateto an overall optical density of 0.45 at 526 nm. When written with 8 mWwrite power a 61 dB CNR was obtained on reading

EXAMPLE 5

In this example the same disk substrate solvent, solution concentration,filter, spin coater, drying conditions, gold deposition process, lacquerlayer application, lamination and testing procedure were used as in thefirst example. Dye 5 was coated on the grooved surface of the substrateto an overall optical density of 0.51 at 526 nm. When written with 9 mWwrite power a 49 dB CNR was obtained on reading.

EXAMPLE 6 Light Stability

The selected dyes were spin coated on 5.08 by 5.08 cm (2 by 2 inch)polycarbonate slides. Optical density measurements were taken 5 mm fromthe edge of the slides with a Hewlett Packard 8450A Diode ArraySpectrophotometer between 300 nm and 800 nm wave lengths. The slide wasexposed through the polycarbonate for sixteen days by a methodrecommended by the Image Stability Technical Center for standard 50 kluxDaylight exposure(ANSI IT9.9-1990 “Stability of Color PhotographicImages” Section 5 Paragraph 5.6 Describes Simulated Indoor IndirectDaylight exposure). After sixteen days the optical densities werere-measured. To calculate the percent optical density loss, from theoptical density value at λ-max before light exposure the optical densityvalue after light exposure was subtracted. The resulting value wasdivided by the optical density value before light exposure andmultiplied by one hundred. Results are presented in Table 3:

TABLE 3 Light Stability % Optical Density Loss After 16 days 50 Dye No.Klux Light Exposure 1 10.2 2 10.6 3 25.1 4 10.1 6 10.5 7 10.6

Table 3 shows the excellent light stability of the recording layersprovided by the invention.

EXAMPLE 7 Dark Stability

The dyes were spin coated on 5.08 by 5.08 cm (2 by 2 inch) polycarbonateslides. Optical density measurements were taken before incubation with aHewlett Packard 8450A Diode Array Spectrophotometer between 300 nm and800 nm wave lengths. The slides were incubated for six weeks in aHotpack Temperature Humidity Chamber (Model 434304) set at 80° C.temperature and 80% relative humidity with the slides placed, dye sideup, in Petri dishes with the tops slightly open. Then opticalmeasurements were taken after six weeks of incubation. To determine thepercent optical density loss, from the optical density value at λ-maxbefore incubation the optical density value after incubation wassubtracted. The resulting number was divided by the optical densityvalue before incubation and multiplied by one hundred to give thepercent loss in optical density as a result of incubation. Results arepresented in Table 4:

TABLE 4 Dark Stability % Optical Density Loss After 6 weeks at Table 1Dye No. 80° C./80% RH 1 4.2 2 3.3 3 22.6 4 5.5

Table 4 shows the excellent dark stability of the optical recordinglayers provided by the invention.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. An optical recording element having a transparent substrate and on the surface of said substrate, a recording layer, a light reflecting layer; wherein the recording layer comprises (a) a metallized azo ether dye having an azo group linking a substituted 3-hydroxypyridine nucleus to a phenyl nucleus wherein the phenyl nucleus has an ether substituent ortho to the azo group and said phenyl nucleus is free of strong electron withdrawing groups and (b) has, when unrecorded, a refractive index at a selected wavelength from 400 to 660 nm, comprising a real part (n) greater than 1.8 and an imaginary part (k) less than 0.3.
 2. An optical recording element having the following layer arrangement: (a) a transparent grooved substrate having a groove width of from 100 to 800 nm; a groove depth of 30 to 270 nm; and a groove pitch of 0.5 to 1.8 μm; (b) a recording layer (i) a metallized azo ether dye having an azo group linking a substituted 3-hydroxypyridine nucleus to a phenyl nucleus wherein the phenyl nucleus has an ether substituent ortho to the azo group and said phenyl nucleus is free of strong electron withdrawing groups and (ii) having, when unrecorded, a refractive index at a selected wavelength from 400 to 660 nm, comprising a real part (n) greater than 1.8 and an imaginary part (k) less than 0.3; (c) a light reflecting layer; (d) an adhesive layer; and (e) a substrate.
 3. The element of claim 2 also comprising a protective layer between layers (c) and (d).
 4. The element of claim 3 also comprising a protective layer between layers (d) and (e).
 5. The element of claim 4 also comprising a reflective layer adjacent to layer (e).
 6. The element of claim 2, having, between layers (d) and (e), the following additional layers in the recited order: a protective layer; a reflective layer; and a recording layer (i) a metallized azo ether dye having an azo group linking a substituted 3-hydroxypyridine nucleus to a phenyl nucleus wherein the phenyl nucleus has an ether substituent ortho to the azo group and said phenyl nucleus is free of strong electron withdrawing groups and (ii) having, when unrecorded, a refractive index at a selected wavelength from 400 to 660 nm, comprising a real part (n) greater than 1.8 and an imaginary part (k) less than 0.3.
 7. The element of claim 1 or 6 wherein the substrate has a thickness of 0.6 mm and a groove pitch of 0.5 to 1.0 μm.
 8. The element of any one of claims 2, 7 wherein the metallized azo ether dye in the recording layer conforms to formula (I):

wherein; R₁ represents hydrogen or an alkyl of from 1 to 6 carbons; R₂ represents hydrogen, an alkyl of from 1 to 6 carbons or alkoxy with 1 to 10 carbons or halogen; R₃ is free of strong electron withdrawing groups and represents hydrogen, an alkyl of from 1 to 10 carbons or alkoxy with 1 to 10 carbons or halogen; R₄ represent an alkyl of from 1 to 10 carbons, a substituted or unsubstituted benzyl; an aryl of from 6 to about 10 carbons or a hetaryl of from 5 to about 10 carbons.
 9. The element of claim 8 wherein the metallized azo ether dye is selected from dyes of Table 1 as follows: TABLE 1 Metallized Azo Ether Dyes

Dye No R₁ R₂ R₃ R₄ 1 H H H CH₃ 2 H H H CH₂CH₃ 3 H H H (CH₂)₇CH₃ 4 H H H (CH₂)₂OCH₂CH₃ 5 H H m-OCH₃ CH₃ 6 H H p-OCH₃ CH₃ 7 H H H

8 H H H (CH₂)₂CH₃ 9 H H H (CH₂)₃CH₃ 10  H H H CH₂CH(CH₃)₂ 11  CH₃ H H CH₂CH₃ 12  CH₃ H H (CH₂)₂CH₃ 13  H CH₂CH₃ H CH₂CH₃ 14  CH₂CH(CH₃)₂ H H CH₂CH₃ 15  H H m-CH₂CH(CH₃)₂ CH₂CH₃


10. The element of claim 9 wherein the metallized azo ether dye is selected from dyes 1, 2, and 3 of Table 1 recited in claim
 9. 